Paper products are used for a variety of purposes. Paper towels, facial tissues, toilet tissues, and the like are in constant use in modern industrialized societies. The large demand for such paper products has created a demand for improved versions of the products.
Generally, the papermaking process includes several steps. An aqueous dispersion of the papermaking fibers is formed into an embryonic web on a foraminous member, such as a Fourdrinier wire, or a twin wire paper machine, where initial dewatering and fiber rearrangement occurs.
In a through-air-drying process, after an initial dewatering, the embryonic web is transported to a through-air-drying belt comprising an air pervious deflection member. The deflection member may comprise a patterned resinous framework having a plurality of deflection conduits through which air may flow under a differential pressure. The resinous framework is joined to and extends outwardly from a woven reinforcing structure. The papermaking fibers in the embryonic web are deflected into the deflection conduits, and water is removed through the deflection conduits to form an intermediate web. The resulting intermediate web is then dried at the final drying stage at which the portion of the web registered with the resinous framework may be subjected to imprinting--to form a multi-region structure.
Through-air drying papermaking belts comprising a reinforcing structure and a resinous framework are described in commonly assigned U.S. Pat. No. 4,514,345 issued to Johnson et al. on Apr. 30, 1985; U.S. Pat. No. 4,528,239 issued to Trokhan on Jul. 9, 1985; U.S. Pat. No. 4,529,480 issued to Trokhan on Jul. 16, 1985; U.S. Pat. No. 4,637,859 issued to Trokhan on Jan. 20, 1987; U.S. Pat. No. 5,334,289 issued to Trokhan et al on Aug. 2, 1994. The foregoing patents are incorporated herein by reference for the purpose of showing preferred constructions of through-air drying papermaking belts. Such belts have been used to produce commercially successful products such as Bounty paper towels and Charmin Ultra toilet tissue, both produced and sold by the instant assignee.
Presently, the resinous framework of a through-air drying papermaking belt is made by processes which include curing a photosensitive resin with UV radiation according to a desired pattern. Commonly assigned U.S. Pat. No. 5,514,523, issued on May 7, 1996 to Trokhan et al. and incorporated by reference herein, discloses one method of making the papermaking belt using differential light transmission techniques. To make a belt comprising a photosensitive resin, a coating of the liquid photosensitive resin is applied to the reinforcing structure. Then, a mask in which opaque regions and transparent regions define a pre-selected pattern is positioned between the coating and a source of radiation, such as UV light. The curing is performed by exposing the coating of the liquid photosensitive resin to the UV radiation from the radiation source through the mask. The curing UV radiation passing through the transparent regions of the mask cure (i.e., solidify) the resin in the exposed areas to form knuckles extending from the reinforcing structure. The unexposed areas (i.e., the areas corresponding to the opaque regions of the mask) remain fluid, i.e., uncured, and are subsequently removed.
The angle of incidence of the radiation has an important effect on the presence or absence of taper in the walls of the conduits of the papermaking belt. Radiation having greater parallelism produces less tapered (or more nearly vertical) conduit walls. As the conduits become more vertical, the papermaking belt has a higher air permeability, at a given knuckle area, relative to a papermaking belt having more tapered conduit walls.
At the same time, in some instances it may be desirable to subject a photosensitive resin to curing at various angles of radiation. For example, it may be desirable to produce a resinous framework having slightly tapered knuckles because such knuckles are more durable under pressure. In other instances, a particular three-dimensional design of a resinous framework may be accomplished by using various angles of radiation.
The current apparatuses for curing the resin to produce the papermaking belts comprising the reinforcing structure and the resinous framework include a radiation source (i.e., a bulb) and a reflector having an elliptical shape. Bulbs of the currently used apparatuses need microwave energy to operate. The elliptical shape of the reflector has been chosen because the elliptical shape and its attendant volume helps to maximize the coupling of microwave energy necessary for the bulbs to operate most efficiently. While the elliptical shape of the reflectors of the prior art is efficient with respect to microwave coupling, the elliptical shape of the reflector generates non-parallel, highly off-axis, or "scattered," rays of radiation. The elliptical shape is thus inefficient for curing the photosensitive resin comprising the framework. So far, as we can determine, the equipment manufacturers have not been able to design a reflector that would maximize microwave energy, and at the same time, generate parallel radiation which could be directed in a certain predetermined direction for the most efficient curing of the resin and, at the same time, produce an acceptable longitudinal uniformity of the radiation. In some cases, space limitations my also influence the shape of the reflector. Therefore, a means of controlling the angle of incidence of the curing radiation independent of reflector's geometry is required.
One of the means of controlling the angle of incidence of the radiation is a subtractive collimator. The subtractive collimator is, in effect, an angular distribution filter which blocks the UV radiation rays in directions other than those desired. A common subtractive collimator comprises a darkcolored metal device formed in the shape of a series of channels through which the light rays may pass in the desired direction. U.S. Pat. No. 5,514,523 cited above and incorporated herein by reference discloses a method of making the papermaking belt utilizing the subtractive collimator.
While the subtractive collimator helps to orient the radiation rays in the desired direction by blocking the rays which have undesired directions, the total radiation energy that reaches the photosensitive resin to be cured is reduced because of loss of the radiation energy in the subtractive collimator.
Therefore, it is an object of the present invention to provide an apparatus for curing a photosensitive resin, which apparatus allows to control an angle of incidence of curing radiation.
It is another object of the present invention to provide an apparatus for curing a photosensitive resin, comprising a plurality of adjustable reflective facets for directing curing radiation in at least one predetermined radiating direction.
It is also an object of the present invention to provide an improved apparatus for curing a photosensitive resin for producing a papermaking belt having resinous framework, which apparatus significantly reduces the loss of the curing energy.
It is a further object of the present invention to eliminate interdependency between the reflector's shape and direction or directions of the reflected radiation.